The opposite nitric oxide modulators do not lead to the opposite changes of metabolites under cadmium excess

Exogenous sodium nitroprusside exhibits multiple positive roles in alleviating cadmium toxicity in tobacco (Nicotiana tabacum L.)

As a donor of the gaseous signaling molecule nitric oxide (NO), sodium nitroprusside (SNP) has been shown to play a positive role in enhancing plant resistance to abiotic stress. However, its role in alleviating cadmium (Cd) toxicity in tobacco (Nicotiana tabacum L.) is not fully understood. This study found that Cd stress significantly inhibited tobacco growth. At the same time, 150 μM SNP was the most effective concentration in alleviating Cd toxicity in seedlings, restoring three stress tolerance indicators-MDA, H2O2, and proline-to control levels. Exogenous SNP mitigated Cd-induced oxidative stress by promoting the accumulation of non-enzymatic antioxidants (total phenolics and flavonoids) and activating key antioxidant enzymes (SOD, CAT, POD, APX, and GR) along with their gene expression. SNP also facilitated Cd accumulation in the root cell wall and prevented Cd translocation from roots to shoots. Additionally, SNP altered Cd's subcellular distribution, promoting its sequestration in vacuoles and cell walls, which may be related to the NO-mediated upregulation of the metallothionein gene NtMT2F and the phytochelatin gene NtPCS2. The addition of SNP significantly increased the proportion of Cd in less toxic chemical forms, with the residual Cd fraction in the Cd + SNP group reaching 7.30 %, higher than the 4.86 % in the Cd-only group. Furthermore, exogenous SNP counteracted Cd's inhibition of nitrate reductase (NR) activity, promoting endogenous NO production. This study systematically reveals the positive roles of exogenous SNP in mitigating Cd toxicity in tobacco, offering valuable insights for producing low-Cd tobacco.

Allantoin overaccumulation enhances production of metabolites under excess of metals but is not tightly regulated by nitric oxide

The aln-3 mutant overaccumulating allantoin and respective wild type (WT) strain of Arabidopsis thaliana were exposed to cadmium (Cd) or mercury (Hg) with or without nitric oxide (NO) donor (sodium nitroprusside, SNP) to study cross-talk, metabolic and oxidative changes between these nitrogen sources (organic vs. inorganic). The aln-3 accumulated over 10-fold more allantoin than WT with the effect of Cd and Hg differing in leaf and root tissue: aln-3 contained more ascorbic acid and phytochelatins when treated with Cd or Hg and more Cd in both organs. SNP depleted leaf Cd and root Hg accumulation in aln3 but had a positive impact on the amount of metabolites typically in WT plants, indicating potentially negative relation between allantoin and NO. In agreement, aln-3 roots showed lower NO signals in control or metal treatments, but higher ROS signal, and SNP had more pronounced impact in WT roots. Flavonol glycosides were more abundant in aln-3 and were affected more by metals than by SNP. Malate was the most affected Krebs acid with strong reaction to SNP and Hg treatment. Data indicate that allantoin overaccumulation influences the accumulation of specific metabolites but nitric oxide has a greater impact on the metabolite profile in WT.

Listeria monocytogenes exposed to antimicrobial peptides displays differential regulation of lipids and proteins associated to stress response

With the onset of Listeria monocytogenes resistance to the bacteriocin nisin, the search for alternative antimicrobial treatments is of fundamental importance. In this work, we set out to investigate proteins and lipids involved in the resistance mechanisms of L. monocytogenes against the antimicrobial peptides (AMPs) nisin and fengycin. The effect of sub-lethal concentrations of nisin and lipopeptide fengycin secreted by Bacillus velezensis P34 on L. monocytogenes was investigated by mass spectrometry-based lipidomics and proteomics. Both AMPs caused a differential regulation of biofilm formation, confirming the promotion of cell attachment and biofilm assembling after treatment with nisin, whereas growth inhibition was observed after fengycin treatment. Anteiso branched-chain fatty acids were detected in higher amounts in fengycin-treated samples (46.6%) as compared to nisin-treated and control samples (39.4% and 43.4%, respectively). In addition, a higher relative abundance of 30:0, 31:0 and 32:0 phosphatidylglycerol species was detected in fengycin-treated samples. The lipidomics data suggest the inhibition of biofilm formation by the fengycin treatment, while the proteomics data revealed downregulation of important cell wall proteins involved in the building of biofilms, such as the lipoteichoic acid backbone synthesis (Lmo0927) and the flagella-related (Lmo0718) proteins among others. Together, these results provide new insights into the modification of lipid and protein profiles and biofilm formation in L. monocytogenes upon exposure to antimicrobial peptides.

Azospirillum brasilense Az39 restricts cadmium entrance into wheat plants and mitigates cadmium stress

In this work, we tested if inoculation with the plant growth-promoting rhizobacteria Azospirillum brasilense strain Az39 alleviates Cd²⁺ stress in wheat seedlings grown under controlled conditions. Growth, total N, N-related metabolites/enzymes, and oxidative stress parameters were measured. Additionally, the usefulness of a real-time PCR protocol to screen the preferred colonization site of the introduced microorganism was evaluated. Inoculated plants demonstrated mitigation of cadmium-induced adverse effects on plant growth and less reactive oxygen species accumulation in their roots by the end of the experiment, 28 days after sowing. Cd addition resulted in lower NO₃^- content in the leaves and higher NO₃^- content in the roots, and a significant rise in NH₄⁺ concentration in both organs in uninoculated plants; in inoculated plants, NH₄⁺ content in the roots did not vary. A. brasilense Az39 enhanced NO levels in wheat root tips, and more adventitious roots and root hairs were observed in inoculated plants. Despite having a more developed root system, inoculated plants showed lower Cd levels in their roots compared to non-inoculated plants. Inoculation with this PGPR favored ion homeostasis in the roots of metal-exposed plants, decreasing Cd/Fe ratio. We corroborated A. brasilense Az39 preference for wheat exorhizosphere using a real-time PCR-based method targeting the nifA gene.

The Possibility of Using Paulownia elongata S. Y. Hu × Paulownia fortunei Hybrid for Phytoextraction of Toxic Elements from Post-Industrial Wastes with Biochar

The potential of the Paulownia hybrid for the uptake and transport of 67 elements along with the physiological response of plants cultivated in highly contaminated post-industrial wastes (flotation tailings—FT, and mining sludge—MS) was investigated. Biochar (BR) was added to substrates to limit metal mobility and facilitate plant survival. Paulownia could effectively uptake and translocate B, Ca, K, P, Rb, Re and Ta. Despite severe growth retardation, chlorophyll biosynthesis was not depleted, while an increased carotenoid content was noted for plants cultivated in waste materials. In Paulownia leaves and roots hydroxybenzoic acids (C6-C1) were dominant phenolics, and hydroxycinnamic acids/phenylpropanoids (C6-C3) and flavonoids (C6-C3-C6) were also detected. Plant cultivation in wastes resulted in quantitative changes in the phenolic fraction, and a significant drop or total inhibition of particular phenolics. Cultivation in waste materials resulted in increased biosynthesis of malic and succinic acids in the roots of FT-cultivated plants, and malic and acetic acids in the case of MS/BR substrate. The obtained results indicate that the addition of biochar can support the adaptation of Paulownia seedlings growing on MS, however, in order to limit unfavorable changes in the plant, an optimal addition of waste is necessary.